CN108137944B

CN108137944B - Room temperature curing highly durable anti-reflective coatings containing nanoparticles

Info

Publication number: CN108137944B
Application number: CN201680057286.4A
Authority: CN
Inventors: 贡特尔·施托尔韦克; 贝恩德·屈内韦格; 克里斯蒂亚娜·施特雷拉特
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2015-10-05
Filing date: 2016-09-23
Publication date: 2020-11-03
Anticipated expiration: 2036-09-23
Also published as: EP3153550A1; EP3359606A1; EP3359606B1; WO2017105576A1; CN108137944A; US20180346734A1

Abstract

In one aspect of the present disclosure, there is provided an antireflective coating composition comprising: (a) hydrophilic spherical silica nanoparticles; (b) hydrophilic elongated silica nanoparticles, wherein the coating composition exhibits a pH value in the range of 7 to 12.5 and the ratio between hydrophilic spherical silica nanoparticles (a) and hydrophilic non-spherical silica nanoparticles (b) is in the range of 10:1 to 1: 10. In another aspect of the present disclosure, there is provided a method for coating a substrate, the method comprising the steps of: (i) providing a substrate having at least one surface; (ii) providing an antireflective coating composition according to the present disclosure; (iii) coating the substrate on at least one surface; (iv) drying the coating, thereby obtaining a coated substrate; wherein step (iv) is carried out at a temperature in the range of from 5 ℃ to 300 ℃.

Description

Room temperature curing highly durable anti-reflective coatings containing nanoparticles

Technical Field

The present disclosure relates to an antireflective coating composition comprising hydrophilic spherical silica nanoparticles and elongated silica nanoparticles in a ratio. The present disclosure further relates to coated substrates. In another aspect, the present disclosure is directed to a method for coating a substrate. In another aspect, the present disclosure relates to the use of such coating compositions and coated substrates.

Background

It has been known since the fortieth of the twentieth century that nanoparticles can be used to obtain anti-reflective coatings (US2,432,484). The optical function of such antireflective coatings is typically achieved by the effective refractive index of the coating being lower than the effective refractive index of the substrate. This causes a gradient between the refractive index of air and the refractive index of the substrate. Thus, the amount of light reflected from the coated substrate is reduced.

At present, based on SiO₂The glass anti-reflective coating of the nanoparticles must be sintered at temperatures above 500 ℃ to obtain a mechanically stable coating over a longer period of time. That is, the antireflective coating is applied at the glass manufacturer before the glass pane enters a tempering oven operating at a temperature above 500 ℃. Thus, tempering the glass and curing or sintering the antireflective coating occur simultaneously.

However, this is desirable when the anti-reflective coating can be applied on an already installed glass substrate such as a solar panel or a greenhouse panel. This is only possible when the antireflective coating is applied by a simple method, which is then able to cure under ambient conditions and provide antireflective properties and ideally some mechanical stability. Furthermore, the antireflective coating composition should exhibit a certain shelf life, which is desirable for field applications.

Disclosure of Invention

In one aspect of the present disclosure, there is provided an antireflective coating composition comprising: (a) hydrophilic spherical silica nanoparticles; (b) hydrophilic elongated silica nanoparticles, wherein the coating composition exhibits a pH value in the range of 7 to 12.5 and the ratio between hydrophilic spherical silica nanoparticles (a) and hydrophilic non-spherical silica nanoparticles (b) is in the range of 10:1 to 1: 10.

In another aspect of the present disclosure, there is provided a method for coating a substrate, the method comprising the steps of:

(i) providing a substrate having at least one surface;

(ii) providing an antireflective coating composition according to the present disclosure;

(iii) coating the substrate on at least one surface;

(iv) drying the coating, thereby obtaining a coated substrate,

wherein step (iv) is carried out at a temperature in the range of from 5 ℃ to 300 ℃.

In another aspect of the present disclosure there is provided a coated substrate comprising a substrate and a coating on at least one surface of the substrate, the coating being obtained by an antireflective coating composition according to the present disclosure or a process according to the present disclosure.

The present disclosure further provides for the use of the antireflective coating composition or coated substrate to improve the light transmittance and/or hydrophilicity of a solar glass panel, a greenhouse glass panel, a window, or a structural glazing of a building or vehicle.

In a further aspect of the present disclosure there is provided the use of an antireflective coating composition or coated substrate for improving crop yield of plants in a greenhouse.

Detailed Description

Before any embodiments of the disclosure are explained in detail, it is to be understood that the disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. As used herein, the terms "a", "an", and "the" are used interchangeably and mean one or more; and "and/or" is used to indicate that one or both of the described conditions may occur, e.g., a and/or B includes (a and B) and (a or B). Also herein, the recitation of ranges by endpoints includes all numbers subsumed within that range (e.g. 1 to 10 includes 1.4, 1.9, 2.33, 5.75, 9.98, etc.). Also, as used herein, the expression "at least one" includes one and all numbers greater than one (e.g., at least 2, at least 4, at least 6, at least 8, at least 10, at least 25, at least 50, at least 100, etc.). Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," "containing," or "having" and variations thereof is meant to be non-limiting, as opposed to the use of "consisting of … …" which is meant to be limiting, and covers the items listed thereafter as well as additional items.

Unless otherwise indicated, the amounts of the ingredients of the composition may be indicated in weight% (or "% wt" or "wt. -%"). The amounts of all ingredients are given as 100 wt% unless otherwise indicated. If the amounts of ingredients are identified in mole%, all ingredient amounts are given as 100 mole% unless otherwise indicated.

All embodiments of the present disclosure may be freely combined, unless explicitly stated otherwise.

A first aspect of the present disclosure is an antireflective coating composition comprising

(a) Hydrophilic spherical silica nanoparticles;

(b) hydrophilic elongated silica nanoparticles;

wherein the coating composition exhibits a pH value in the range of 7 to 12.5 and the ratio between the hydrophilic spherical silica nanoparticles (a) and the hydrophilic non-spherical silica nanoparticles (b) is in the range of 10:1 to 1: 10.

The coating composition can exhibit good shelf life and ease of processing. When coated on a substrate, preferably glass, coatings are obtained which can be used as anti-reflective coatings. For example, when coated on a glass panel or sheet, the coating from the coating composition may increase the transmission of light through the sheet or panel, and may additionally exhibit desirable characteristics such as good abrasion resistance and/or aging resistance and may even cause high hydrophilicity.

The coating composition comprises silica nanoparticles. The silica nanoparticles comprise silica, preferably at least 90% by weight silica. Nanoparticles contemplated herein are particles having a length of less than 1000nm, more preferably less than 500nm, even more preferably less than 350 nm. The size of the nanoparticles can be determined by spreading a thin dispersion of particles on the surface and measuring the size of the individual particles using microscopic techniques, preferably Scanning Electron Microscopy (SEM) or Atomic Force Microscopy (AFM). Preferably, the average size is determined by measuring the size of at least 100 individual particles. The aspect ratio is the ratio between the length and the width of the particle. For elongated nanoparticles as contemplated herein, the length is the maximum distance between two points in the particle and the width is the maximum diameter measured perpendicular to the central axis of the particle. Both length and width are measured from the projection of the particles observed under the microscope.

A coating composition as described herein comprises (a) spherical silica nanoparticles. As used herein, "spherical" means substantially spherical, i.e., spherical silica nanoparticles having an average aspect ratio of about 1:2 or less, preferably about 1:1 or less. Preferably, the nanoparticles have an average particle size in the range of 1nm to 20nm, more preferably 3nm to 15 nm. Generally, the spherical nanoparticles used herein are provided in a solvent, preferably as a dispersion, more preferably as an aqueous dispersion. One example of a hydrophilic spherical silica nanoparticle is Nalco 1115 (Nalco inc.) that contains 15% colloidal SiO₂。

In addition, a coating composition as described herein comprises (b) elongated silica nanoparticles. Elongated nanoparticles contemplated herein are generally non-spherical nanoparticles, i.e., wherein one diameter of a particle is offset from another diameter of the same particle. Typically, the elongated nanoparticles have a larger aspect ratio than the spherical nanoparticles, preferably in the range of 1:2.5 to 1:20, more preferably in the range of 1:4 to 1: 7. An example of hydrophilic elongated silica nanoparticles is Snowtex stock (Nissan Chemical) which comprises from 15 to 16 wt% amorphous SiO₂。

The silica nanoparticles used herein are generally hydrophilic, i.e. they have a polar surface, or even a negative or positive surface charge, preferably a negative surface charge. Silica nanoparticles as used hereinThe surface of the particles is not substantially modified by organic compounds having reactive groups capable of crosslinking, such as acrylates, methacrylates, vinyl species, or epoxy resins. In addition, the surface of the silica nanoparticles used herein is also not activated by surface modifiers such as alkoxysilanes, alkoxy zirconates, alkoxy aluminates, and the like. The use of hydrophilic silica nanoparticles without any additional reactive groups as described above in combination with a pH as described herein provides an antireflective coating composition as described herein. In particular, the antireflective coating composition is capable of forming a coating with substantial mechanical stability after the application has been applied and cured at ambient conditions without requiring elevated temperatures or requiring additional tempering of the coating, i.e., the coating and the coated substrate. This has the advantage that the coating composition according to the present disclosure can be applied directly on site on a substrate, for example on an already built solar panel or greenhouse panel. Thus, the coating composition according to the present disclosure has advantageous processability, long shelf life, and provides a coating in a safe and easy manner that can exhibit a desirable combination of properties, such as anti-reflective optical properties, mechanical properties such as abrasion resistance (even after weathering conditions), and provide a substrate with a hydrophilic surface. Without wishing to be bound by theory, it is postulated that upon curing, the Si-OH groups present on the surface of the silica nanoparticles react with each other to form Si-O-Si bonds linking the different nanoparticles. Thus, it may additionally be assumed that this may form a network between different nanoparticles. Further, it can be hypothesized that Si-O-Si bonds can form between the silica nanoparticles and the glass or ceramic substrate (which also comprises SiO) of the coating compositions described herein₂And may have Si-OH groups on its surface). Thus, a tight connection between the coating and the substrate can be obtained upon curing, even when cured only at ambient temperature for a period of time such as 24 hours or less.

With regard to the size of the nanoparticles, it is preferred that the nanoparticles (b) have a diameter on the main axis of less than 200nm, preferably less than 150nm, and that the nanoparticles (a) have a diameter of less than 100nm, preferably less than 50 nm.

Coating compositions according to the present disclosure generally exhibit a pH in the range of 7 to 12.5, preferably in the range of 8 to 11.5, more preferably in the range of 8.5 to 11. Alternatively, the pH of the composition according to the present disclosure may have a pH in the range of 11 to 12.5. It was found that maintaining the pH of the composition according to the present disclosure within these ranges may have the following effect: enhanced shelf life of the composition, i.e. a certain resistance to ageing, and enhanced properties of the coating obtained from the composition described herein. However, lowering the pH of the composition below the lower limits described above, for example a pH of 2 to 4, will result in a significant reduction in the shelf life of the composition.

As far as different nanoparticles are used, it is preferred that the ratio between the hydrophilic spherical silica nanoparticles (a) and the hydrophilic elongated silica nanoparticles (b) is in the range of 5:1 to 1:5, preferably in the range of 3:1 to 1:3, more preferably in the range of 2:1 to 1:2, even more preferably in the range of 1:1 to 1:2.

When a preferred ratio between hydrophilic spherical silica nanoparticles (a) and hydrophilic elongated silica nanoparticles (b) is used, a coating in which the above-mentioned effects are specifically present can be obtained. For example, the transmission of light through the coating and, for example, a float glass panel coated with the coating can be enhanced.

It is preferred that the coating composition of the present disclosure further comprises (c) a polysilicate. The effect of adding polysilicate to the composition is that the coating obtained from the composition may exhibit enhanced and reproducible mechanical properties such as wear resistance. Preferably, the polysilicate is of formula M₂(SiO₂)_nPolysilicate of O, wherein M is selected from Li, Na, K, preferably Li or Na, more preferably Li, and n is an integer between 2 and 15, preferably between 4 and 9. It is also preferred that the polysilicate is used as dissolved in a solvent, preferably water. For example, of the formula Li₂Si₅O₁₁The polysilicate of (2) can be obtained from the Hansa Group (Hansa Group) as a 20% solution in water (CAS-Nr.12627-14-4).

It is further preferred that the coating composition according to the present disclosure further comprises (d) an organic compound, preferably wherein the organic compound is selected from polysaccharides, proteins and polyvinyl alcohols, preferably from natural and modified polysaccharides, preferably from the list consisting of: xanthan gum, carrageenan, pectin, gellan gum, xanthan gum, diurea, cellulose ethers such as carboxymethyl cellulose, methyl cellulose, ethyl cellulose and hydroxyethyl cellulose. The addition of at least such organic compounds may result in an even more uniform coating obtained from the composition, as well as better processability of the composition, especially when the substrate is coated by spraying or by a doctor blade. Without wishing to be bound by theory, a more uniform coating may result from a viscosity increase upon drying. Thus, the organic compound (d) may be used as a rheology modifier in the composition according to the present disclosure. Examples of organic compounds (d) that may be advantageously used in the coating compositions described herein are xanthan gum (available from Jungbunzlbauer) and Keltrol BT (available from sbackacao corporation (CP Kelco)).

Preferably, the coating composition according to the present disclosure further comprises (e) a solvent. The solvent will generally improve the processability of the coating composition, for example by applying the coating composition to a substrate using a spray, doctor blade or brush. Polar solvents are generally preferred due to the nature of the components of the coating composition. Preferably, the solvent comprises at least one solvent selected from the list consisting of alcohols and water, preferably at least one alcohol and/or water, more preferably essentially consisting of water. Examples of alcohols are ethanol, propanol, butanol, isobutanol and tert-butanol, and mixtures thereof. For example, the solvent may consist of a mixture of ethanol and water. The ratio of ethanol and water can be adapted to the compound used, the chosen application method, the substrate, the drying method and to price and time issues. In this regard, it is more preferable to use water as the solvent (d), in which an additional trace amount of alcohol such as ethanol may be contained. The use of water is particularly useful for applications as an after-market make-up coating on solar panels and greenhouses that can be manually applied by the user.

With respect to the amounts of components (a) to (d), it is preferred that the coating composition comprises:

(a) hydrophilic spherical silica nanoparticles in an amount of 15 to 85 wt. -%, preferably 25 to 70 wt. -%, more preferably 30 to 55 wt. -%, relative to the total weight of the solids content of the coating composition;

(b) hydrophilic spherical silica nanoparticles in an amount of 15 to 85 wt. -%, preferably 25 to 70 wt. -%, more preferably 40 to 70 wt. -%, relative to the weight of the solids content of the coating composition;

(c) optionally, a polysilicate in an amount of 1 to 25 wt. -%, preferably 5 to 15 wt. -%, relative to the total weight of the solids content of the coating composition;

(d) optionally, an organic compound in an amount of 0.01 to 5 wt. -%, preferably 0.02 to 3 wt. -%, more preferably 0.04 to 1.6 wt. -%, relative to the total weight of the solids content of the coating composition, and

(e) optionally, a solvent.

The effects described herein become particularly apparent when the coating composition comprises ingredients within the above ranges and preferred ranges. It will be appreciated that the concentration of the coating composition may be adapted to the particular use provided that the pH of the composition is in the range of 7 to 12.5, in particular in the preferred and more preferred ranges.

Additionally, the coating composition according to the present disclosure may comprise (f) a surfactant, preferably an anionic surfactant. Surfactants can improve the wettability of substrates, especially glass surfaces, and especially on non-activated surfaces. Preference is given to compounds of the formula C_nH_2n-1SO₃Na, wherein n is from 10 to 20, preferably from 14 to 16. As an example of a surfactant (f) that can be used in the coating compositions described herein, Hansanyl OS (10% solution) available from the Hansa group (CAS-Nr.68439-57-6) can be mentioned.

The coating compositions according to the present disclosure may be used to coat the surface of a substrate. Accordingly, the present disclosure additionally provides a method for coating a substrate, the method comprising the steps of:

(i) providing a substrate having at least one surface;

(ii) providing a curable composition according to the present disclosure;

(iii) coating the substrate on at least one surface;

(iv) drying the coating, thereby obtaining a coated substrate,

The coating may be applied in step (iii) by any known wet coating deposition process, such as spin coating, dip coating, spray coating, flow coating, meniscus coating, knife coating, capillary coating and roll coating. Thus, depending on the substrate, the scale (i.e. the area to be coated), and other factors, application may be performed using, for example, a meyer rod, a brush, spray, dip, kiss, a roller bar, or a knife. For example, coating a substrate in a factory on a large scale may provide completely different possibilities than, for example, coating the surface of a solar panel already installed on site or coating the outer or inner surface of a glass panel of a greenhouse, as the skilled person will know. Thus, the coating in step (iii) may be performed by a paint brush, knife, spray device or roller bar while the field application on an already installed solar panel or greenhouse panel is in progress. This means that the application can be carried out in a simple, safe and convenient manner, preferably even by untrained personnel. For the application in step (iii), the coating composition preferably used in the process described herein comprises (e) as a solvent as described above. The thickness of the coating applied in step (iii) may be adapted to the envisaged use of the coated substrate, however it is strongly preferred to carry out the coating at least to the thickness required to provide the substrate with at least some anti-reflective properties. For example, the coating composition may be applied to a wet film thickness in the range of 1 μm to 300 μm, preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm. With respect to the dry film thickness, it is preferred to obtain a coating having a thickness in the range of 5nm to 300nm, preferably in the range of 10nm to 180nm, more preferably in the range of 15nm to 130 nm. The skilled person will know that while a low dry film thickness (e.g. in the range of 5nm to 50 nm) is sufficient to obtain a coating exhibiting hydrophilic properties, leading to e.g. antifouling effects, the optimum dry film thickness for obtaining the desired optical properties, such as antireflection effects, is in the range of 70nm to 150nm, preferably in the range of 80nm to 120 nm.

The substrate used in the method according to the present disclosure has at least one surface that can be coated with a coating composition. Since the coating obtained in this process has anti-reflective properties, the skilled person will know that the substrate is selected for the desired anti-reflective properties. In this regard, it is preferred that the substrate is selected from the group consisting of polymeric materials, glass, metal, wood, ceramics, preferably glass and metal, more preferably glass and ceramic, and even more preferably glass. Glass is particularly preferred since the obtained coating, due to its anti-reflective properties, may cause an increase in the transmission of light, in particular visible light, through the glass, in particular a glass film, panel or sheet. The glass may be tinted or colored, however, in most cases uncolored glass is preferred because maximum light transmission through the substrate is desired. The metal substrate may be used for applications in the automotive industry or for making panels or sheets for applications in residential construction. Ceramics can be used for the same applications as metal substrates. With respect to metal, wood and ceramic materials, the optical properties of the coatings obtained according to the present disclosure are of lesser importance, however the hydrophilic nature of the coatings described herein can provide metal, wood and ceramic substrates with desirable antifouling properties. The same applies to polymeric materials. As for the polymer material, a material exhibiting good light transmission characteristics is preferable. Applications of the polymeric substrate coated on at least one surface may include sun visors for helmets, windshields or windows for vehicles (such as automobiles, airplanes, helicopters, trains, boats or ships), screens for televisions, computers, mobile phones, displays, and architectural windows. The substrate may have any form, provided that it has at least one surface, wherein any of anti-reflective, hydrophilic and anti-fouling properties are desired. That is, the substrate forms may include shaped articles, sheets, films, and panels. Preferred forms are sheets, films and panels, in particular glass sheets, films and panels, which are especially useful for applications in solar panels and greenhouses.

In step (iv), the coating obtained by coating at least one surface of the substrate with the coating composition described herein is dried. Drying may be performed by any method known in the art, for example by exposing the object to elevated temperatures and/or applying a stream of air, preferably dry air, or by merely allowing the coating to dry under ambient conditions. That is, drying is carried out at a temperature in the range of 5 ℃ to 300 ℃, including, for example, drying the coating at ambient temperature. That is, the drying may be preferably performed at a temperature in the range of 3 ℃ to 50 ℃, preferably at a temperature in the range of 4 ℃ to 35 ℃, more preferably at a temperature in the range of 5 ℃ to 25 ℃. The coating composition can be dried at ambient conditions, i.e. ambient temperature, and a coating of sufficient mechanical and/or antireflective and/or hydrophilic character is obtained. With respect to drying time, it is understood that the time required to obtain a fully cured coating is related to the temperature applied. However, a coating with sufficient mechanical stability for further processing can be obtained after 5 hours, after 2 hours or even after 1 hour after drying under ambient conditions as described above. A fully cured coating can be obtained after 24 hours at ambient temperature as described above. This is very advantageous for coating field applications, for example at installed solar panels or panels of greenhouses.

That is, the coating can be applied on the solar panel and the greenhouse at ambient conditions on the site where the solar panel or the greenhouse is located. Thus, the method according to the present disclosure and the coating composition according to the present disclosure are particularly advantageous for users who wish to provide an effective and robust anti-reflective and/or hydrophilic coating to their already existing or installed solar panels or greenhouse panels. Drying at a temperature above ambient temperature, for example in the range of 80 ℃ to 300 ℃, may be carried out, although drying at ambient temperature, for example in the range of 5 ℃ to 50 ℃, is sufficient to obtain a coating with sufficient mechanical and/or anti-reflective properties. This may have the effect of shortening the drying time and, if desired, may have the additional effect of improving mechanical properties such as scratch and abrasion resistance of the coating. This can be used to coat substrates on a large or industrial scale, such as in the manufacturing processes of panels, sheets and films, in particular solar panels, greenhouse panels, windshields, windows and displays.

The process may further comprise an additional step (iv) of tempering the coated substrate obtained in step (iii) at a temperature in the range of 300 ℃ to 800 ℃, preferably in the range of 400 ℃ to 600 ℃. This may have the effect of improving mechanical properties such as the scratch resistance of the coating obtained in step (iii), if desired.

Another aspect of the present disclosure is a coated substrate comprising a substrate and a coating on at least one of a surface of the substrate, the coating being obtained from a composition according to the present disclosure or by a method according to the present disclosure. With respect to the substrate, coating composition, and method, it is understood that the foregoing substrate, coating composition, and method described herein apply.

Specifically, it is preferable that the substrate is a shaped article of a panel, a sheet, a film. Due to its nature it is further preferred that the coated substrate is part of a solar panel, a display, a window, a windshield, goggles or a greenhouse.

The coating of the coated substrate described herein may exhibit certain antireflective, hydrophilic and/or mechanical properties. The antireflective properties considered herein produce another effect, namely an increase in the transmission of light through a substrate, such as a float glass panel. The transmission properties as considered were according to ASTM D-1003 or DIN EN9050 (published in 2003). Preferably, the coating exhibits a dT of at least 1.0%, preferably at least 1.4%, more preferably at least 1.8%, and even more preferably at least 2.0% according to DIN EN 9050. This has the effect that the transmission of light through a float glass panel, for example used in a solar panel or a greenhouse, may increase by at least 2%. An increase in light transmittance in this amount means a significant improvement in the application of light directly converted into energy, plant growth or otherwise utilizing light. For example, the output of the solar panel module may increase by 2% to 3%. Similarly, the productivity in plant production is directly dependent on the supply of sunlight. Therefore, high optical transparency of the covering windows, ceilings or wall panels of a greenhouse is very important. For example, a 2% increase in light transmission through the ceiling and walls of a greenhouse can directly result in an increase of 2% in the crop yield of the greenhouse, such as in the case of tomatoes, which is considered to be a significant improvement. Further, the coating of the coated substrate described herein can exhibit hydrophilic properties. In this regard, the coating preferably exhibits a static water contact angle according to ISO 14989 (published 2004) of 20 ° or less, preferably 10 ° or less, more preferably 7 ° or less, even more preferably 5 ° or less. This has the effect that when moisture precipitates on the coating, surface wetting rather than water droplet formation can occur. This will lead to important effects for a variety of applications. For example, light transmission through, for example, a glass panel can be compromised by light scattering from the formation of water droplets. Thus, a hydrophilic coating as described herein may have the advantage that wetting of its surface may instead occur, so that the formation of water droplets may be avoided and thus the loss of light transmittance by scattering may be avoided to a certain extent. This is especially important for the same applications as mentioned above, especially solar panels and greenhouse panels. In this regard, it is preferred that the coated substrate is a glass panel that is coated on at least one substrate and will subsequently form the outer surface of the panel (e.g., the outer surface of a solar panel and a greenhouse panel, respectively).

In another preferred embodiment, the coated substrate is coated on two opposite sides of the substrate. In this regard, it is particularly preferred that the coated substrate is a glass panel, film or sheet, coated on two opposing substrates thereof. Again, this is particularly useful for applications in greenhouses. For example, if moisture settles in the form of droplets on the underside of the ceiling or window of a greenhouse, the droplets can descend in an uncontrolled manner to the plants below. As a result, the plants become moist, which is generally undesirable in greenhouses. Thus, the formation of water droplets on a greenhouse ceiling can be avoided when the underside (i.e., "interior") of the glass panels forms the ceiling or ceiling window of the greenhouse coated with the coatings described herein. As a result of the wetting of the coating surface, the large surface of the ceiling becomes wet as the moisture settles, so that the settled moisture travels along the panel surface and can subsequently be drained off in a controlled manner. Thus, when a coating according to the present disclosure is present in a greenhouse, both an increase in light transmittance and an avoidance of uncontrolled droplet formation can be achieved, which is particularly advantageous.

Furthermore, the coating of the coated substrate according to the present disclosure may exhibit advantageous mechanical properties in terms of wear resistance according to DIN EN 1096-2 (published in 2012). Specifically, according to the above specifications, the wear test may be performed by employing a force of 10N and a speed of 60 cycles/minute, deionized water and a 3M high performance microfiber wipe 2010, and using 3000 cycles. It is preferred that the coated glass substrate exhibits a dT drop of less than 1% after the above abrasion test conditions according to DIN EN9050 (published in 2003).

Similarly, the coating of the coated substrate according to the present disclosure may exhibit advantageous properties in terms of weather resistance conditions, such as QUV according to the accelerated weathering test, according to ASTM G154-6 (published under 2012). Similar to abrasion resistance, the coating of a glass substrate coated as described herein may exhibit a dT reduction of less than 1%, preferably less than 0.8%, more preferably less than 0.6% according to DIN EN9050 (published in 2003).

Due to the characteristics of the coating composition and the coated substrate according to the present disclosure, another aspect of the present disclosure is the use of the coating composition or the coated substrate for improving the light transmittance and/or hydrophilicity of a solar glass panel, a greenhouse glass panel, a window, or a glazing for structural windows of buildings or vehicles.

Examples

The present disclosure is further described, but is not intended to be limited thereto. The following examples are provided to illustrate certain embodiments and are not intended to be limiting in any way. Before this, certain test methods for characterizing materials and their properties will be described.

Abbreviations：

RT: at room temperature

h: hours;

min: the method comprises the following steps of (1) taking minutes;

n: newton

n.d.: not determined

Ex.: examples

Ex.: comparative example

Use of ingredients

Naerceae 1115: silica nanoparticle dispersions from Nalco inc (Nalco inc.), colloidal SiO with aspect ratio 1:1 (spherical), average particle size 4nm, and solids content 15%₂pH 10 to 11, solvent water.

Snowtex ST-OUP: dispersion of silica nanoparticles from Nissan Chemical having an aspect ratio of 1:2.7 to 11.1 (non-spherical, elongated), an average particle diameter of 9nm to 15nm/40nm to 100nm, and a solids content of 15% to 16% amorphous SiO₂pH 2 to 4, solvent ═ water.

Li-sodium polysilicate: li from Sigma Aldrich₂Si₅O₁₁And a solids content of 20% to 25%.

Keltrol BT: xanthan gum from Spanish Kelco (CP Kelco)

Hansanyl OS: c14-16 sulfonate from Hansa Group

Method of producing a composite material

Preparation of：

The coating solution was prepared by mixing the ingredients shown in table 1 in a container at room temperature while stirring for about 1 hour.

Applications of：

The coating solution was applied as a fresh coating solution and an aged solution on float glass using a 5 μm meyer rod. After drying and curing at ambient temperature, the coated glass samples were kept at room temperature for 24 hours before any further use.

Aging of：

The AR coating solution was stored in an oven at 65 ℃ for 14 days. The solution was conditioned at room temperature for at least 2 hours before further use.

Wear testing：

Wear tests were performed on a 5900 reciprocating grinder (Taber Industries). The wear was tested by applying a force of 10N and a speed of 60 cycles/min. Wet abrasion was performed with deionized water. A 3M high performance microfiber tape 2010 was used in the wiping. 3000 cycles were performed.

Transmission performance：

Transmittance testing was performed as indicated using a Hunterlab Ultra Scan XE or a Perkin Elmer Lambda 1050UV/vis/IR photometer. The samples were measured following DIN EN9050 (published in 2003). The reported values are the average of at least 3 individual measurements.

Pressure cooker resistance：

The forced pressure cooker test was performed at T-120 ℃. The test was for up to 8 hours, the transmission was measured every 2h as taken from a climatic chamber (no cleaning or wiping).

Damp and heat resistance (DH)：

The test was carried out in accordance with DIN EN 61215 (published in 2005). The climate chamber has 85% relative humidity, 85 ℃ and 1000 h. The reported values are the average of at least 5 different glass sheets with 5 measurements.

QUV testing (accelerated weathering)

Cycle 1 was tested according to ASTM G154-6 (published in 2012). 1000h, 8h0.89W/cm at 60 DEG C²(ii) a Condensation was carried out at 50 ℃ for 4h, 3 measurements. The testing device comprises: QLAB type QUV nebulizer.

QUV test with nebulizer (accelerated weathering)：

Testing was performed according to ASTM G154-6. At 60 ℃ for 15 minutes, 8h0.89W/cm²Without heating, was condensed at 50 ℃ for 3.75h, 3 measurements. The testing device comprises: QLAB type QUV nebulizer.

Static contact Angle (Water)。

The tests were carried out according to ISO 15989 (published in 2004) in the following procedure: contact angles were measured using a Goniometer ERMA contact angle meter G-1:3 μ l drop applied to the surface at 23 ℃. The contact angle was measured after 20 seconds. The sessile drop method was used with the Populus-Laplace method and a contact angle system OCA from Dephco (dataphysics) model OCA 15 Pro.

Composition of：

Table 1: compositions according to the examples and comparative examples. Values are given in weight percent of solid compound relative to the total weight of the combined solids content of the composition.

Table 2: compositions according to the examples and comparative examples. Values are given in weight% relative to the total weight of the composition.

The composition according to the examples was then applied to the surface of the glass sample as described above. The test was additionally performed as described above. The test results are shown in tables 3 to 7 below.

In table 3, the transmittance of samples coated with the compositions according to example 1, example 2, example 3, example 4 and example 5 and uncoated samples of float glass was tested according to Hunterlab Ultra Scan XE and the measurement conditions described herein. It should be noted that the values should be observed with respect to each other, i.e. to allow comparison between the various samples measured herein.

Table 3: transmittance test from 360nm to 750 nm.

As shown in table 3, an increase in transmittance of the coated samples was obtained compared to the uncoated samples.

Fresh coating composition and coating composition aged for a period of time as described above are also applied as described above. The initial transmittance increase (dt) relative to the uncoated float glass sample was measured with a Perkin Elmer Lambda 1050UV/vis/IR photometer after drying at room temperature for 24 h. In addition, dT was measured after the wear test was performed. As a comparative example, a 3M GC 200 coating composition was used. It must be noted at this point that the GC 200 generally needs to be cured at elevated temperatures. Nevertheless, to compare the results with the samples according to the present disclosure, the GC 200 was dried using only the same procedure, i.e., at room temperature for 24 h. The results are summarized in table 4.

Table 4: dT after aging and after wear test procedure.

The test samples obtained from the coating composition according to example 6 were tested for the increase in transmittance relative to an uncoated sample of float glass. Next, the coating samples of example 6 were subjected to the test conditions for damp heat, pressure cooker, abrasion, QUV (with sprayer) and shelf life testing according to the test methods described herein. The results are summarized in table 5 below. The% T reduction refers to the reduction in transmission compared to the transmission of the same sample before being subjected to aging conditions such as damp heat or pressure cooker.

Table 5: aging test conditions for samples coated with the composition according to example 6.

The water contact angle of an uncoated float glass sample was measured and compared to a sample coated with the composition according to example 6. The results are summarized in table 7 below. Water contact angles of 5 ° and below indicate strong hydrophilicity.

Table 7: and (4) testing the water contact angle.

Next, the contamination test was performed as follows: the chamber (dimensions 10cm x 30cm x 40cm) was filled with arizona sand (arizona test dust nominally 0 microns to 70 microns). A sample of uncoated float glass was inserted into the chamber, after which the chamber was purged with a nitrogen atmosphere so that a low relative humidity (about 20%, corresponding to desert conditions) was achieved. Thereafter, the box was shaken for about 1 minute. The cartridge was opened and the sample visually inspected with the naked eye. The same procedure was repeated with samples coated with the coating composition according to example 6. The samples were compared and it was found that when the sample with the coating of example 6 had a clean surface, the surface of the untreated sample was not clean, i.e. covered with a fine sand layer.

Claims

1. An antireflective coating composition comprising:

(a) hydrophilic spherical silica nanoparticles;

(b) hydrophilic elongated silica nanoparticles;

(c) formula M₂(SiO₂)_nPolysilicate of O, wherein M is selected from Li, Na, K and n is an integer between 2 and 15; and

(d) a solvent, the solvent comprising water,

wherein the coating composition exhibits a pH in the range of 7 to 12.5 and the ratio between the hydrophilic spherical silica nanoparticles (a) and the hydrophilic non-spherical silica nanoparticles (b) is in the range of 10:1 to 1: 10; and

wherein the surface of the silica nanoparticles is not modified with an organic compound having a reactive group capable of crosslinking and is also not activated by a surface modifier.

2. The antireflective coating composition of claim 1, where in formula M₂(SiO₂)_nIn the polysilicate of O, n is an integer between 4 and 9.

3. The antireflective coating composition of claim 1, where the ratio between the spherical nanoparticles (a) and the elongated nanoparticles (b) is in the range of 5:1 to 1: 5.

4. The antireflective coating composition according to claim 3, wherein the ratio between the spherical nanoparticles (a) and the elongated nanoparticles (b) is in the range of 3:1 to 1: 3.

5. The antireflective coating composition of claim 3, where the ratio between the spherical nanoparticles (a) and the elongated nanoparticles (b) is in the range of 2:1 to 1:2.

6. The antireflective coating composition according to claim 3, wherein the ratio between the spherical nanoparticles (a) and the elongated nanoparticles (b) is in the range of 1:1 to 1:2.

7. The antireflective coating composition according to any one of claims 1 to 6, where the coating composition is curable at a temperature in the range of from 3 ℃ to 50 ℃.

8. The antireflective coating composition according to claim 7, where the coating composition is curable at a temperature in the range of from 4 ℃ to 35 ℃.

9. The antireflective coating composition according to claim 7, where the coating composition is curable at a temperature in the range of from 5 ℃ to 25 ℃.

10. The antireflective coating composition according to claim 7, wherein the diameter of the nanoparticles (b) is less than 200nm on the major axis and the diameter of the nanoparticles (a) is less than 100 nm.

11. The antireflective coating composition of claim 10, where the diameter of the nanoparticles (b) is less than 150nm on the major axis.

12. The antireflective coating composition according to claim 10, wherein the nanoparticles (a) have a diameter of less than 50 nm.

13. The antireflective coating composition of claim 1, further comprising (e) an organic compound.

14. The antireflective coating composition according to claim 13, wherein the organic compound is selected from the group consisting of polysaccharides, proteins, and polyvinyl alcohol.

15. The antireflective coating composition according to claim 13, wherein the organic compound is selected from natural and modified polysaccharides.

16. The antireflective coating composition according to claim 14, wherein the polysaccharide is selected from the list consisting of: carrageenan, pectin, gellan gum, xanthan gum, diurea, and cellulose ethers.

17. The antireflective coating composition of claim 16, wherein the cellulose ether is selected from the group consisting of carboxymethyl cellulose, methyl cellulose, ethyl cellulose, and hydroxyethyl cellulose.

18. The antireflective coating composition of claim 13, where the coating composition comprises:

(a) spherical nanoparticles in an amount of 15 to 85 wt.%, relative to the total weight of the solids content of the coating composition;

(b) non-spherical nanoparticles in an amount of 15 to 85 wt.%, relative to the total weight of the solids content of the coating composition;

(c) optionally, a polysilicate in an amount of 1 to 25 wt.%, relative to the total weight of the solids content of the coating composition;

(d) optionally an organic compound in an amount of 0.01 to 5 wt. -%, relative to the total weight of the solids content of the coating composition, and

(e) optionally, a solvent.

19. The antireflective coating composition according to claim 18, wherein the coating composition comprises spherical nanoparticles in an amount of from 25 to 70 wt% relative to the total weight of the solids content of the coating composition.

20. The antireflective coating composition according to claim 18, wherein the coating composition comprises spherical nanoparticles in an amount of from 30 to 55 wt% relative to the total weight of the solids content of the coating composition.

21. The antireflective coating composition according to claim 18, wherein the coating composition comprises non-spherical nanoparticles in an amount of from 25 to 70 wt% relative to the total weight of the solids content of the coating composition.

22. The antireflective coating composition according to claim 18, wherein the coating composition comprises non-spherical nanoparticles in an amount of from 40 to 70 wt% relative to the total weight of the solids content of the coating composition.

23. The antireflective coating composition according to claim 18, wherein the coating composition optionally comprises polysilicate in an amount of 5 to 15 wt. -%, relative to the total weight of the solids content of the coating composition.

24. The antireflective coating composition according to claim 18, wherein the coating composition optionally comprises an organic compound in an amount of from 0.02 to 3 wt% relative to the total weight of the solids content of the coating composition.

25. The antireflective coating composition according to claim 18, wherein the coating composition optionally comprises an organic compound in an amount of from 0.04 to 1.6 wt% relative to the total weight of the solids content of the coating composition.

26. A method for coating a substrate, the method comprising the steps of:

(i) providing a substrate having at least one surface;

(ii) providing the antireflective coating composition of claim 1;

(iii) coating the substrate on at least one surface;

(iv) drying the coating, thereby obtaining a coated substrate,

27. The method of claim 26, wherein the substrate is selected from the group consisting of polymeric materials, glass, metals, wood, and ceramics.

28. The method of claim 26, wherein the substrate is selected from the group consisting of glass and metal.

29. The method of claim 26, wherein the substrate is selected from the group consisting of glass and ceramic.

30. The method of claim 26, wherein the substrate is selected from glass.

31. A coated substrate comprising a substrate and a coating on at least one surface of the substrate, the coating being obtained from the antireflective coating composition according to claim 1 or by the process according to claim 26.

32. The coated substrate of claim 31, wherein the substrate is a panel, sheet, shaped article, or film.